docs: improve CI and testing documentation (#21202)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sgl-kernel/tests/test_per_token_quant_fp8.py

@@ -1,4 +1,5 @@
 import itertools
+import sys
 from typing import Optional, Tuple
 
 import pytest
@@ -54,4 +55,4 @@ def test_per_token_quant_compare_implementations(
 
 
 if __name__ == "__main__":
-    pytest.main([__file__])
+    sys.exit(pytest.main([__file__]))